1. Field of the Invention
The present invention pertains to a belt conveyor system in a plant for treatment of food products.
2. Description of the Prior Art
Plants for treatment of food products using hot or cold air, including steam, in order to cook, heat, dry, moisture, chill, refrigerate or freeze the food products are known. In an advantageous arrangement, such plants include a belt conveyor system comprising an endless conveyor belt following, through part of its length, a helical path section and a preceding straight path section. Also, the helical path section is often followed by another straight path section, the two straight path sections being interconnected by a return path section.
An endless conveyor belt can comprise transverse elements, e.g. rods, interconnected by links disposed along opposite lateral edges of the belt. The successive links at each side of the belt may be mutually slideable in the longitudinal direction of the belt such that the belt is permitted to follow lateral curves in both directions.
Other endless belts for use in an air treatment plant including a helical path section have links at one lateral edge of the belt which are not mutually slideable but define a constant pitch, e.g. as disclosed in U.S. Pat. Nos. 4,867,301 to Roinestad and 4,878,362 to Tyree.
Conveyor belts having a sliding action between the links at both lateral edges of the belt experience collapsing or contraction of the links along the inside lateral edge of the belt in the helical path section. More precisely, when the belt reaches a point of transition between the helical path section and the preceding straight path section, the links at the inner lateral edge of the belt slide towards each other so as to present a reduced pitch, while the links at the outer lateral edge of the belt either retain the same pitch or expand by sliding away from each other to a greater pitch than along the preceding straight path section.
The collapsing or contraction of a conveyor belt used for food products is disadvantageous in that delicate food products, such as meat patties and fish filets, loaded on the belt upstream of the point of transition, may adhere to or be damaged by the collapsing belt or even come into contact with each other. As a result, the appearance of the food products may be deteriorated or they may be difficult to unload from the belt.
Using conveyor belts of the type having links at the inner lateral edge which retain a constant pitch eliminates collapsing of the belt at said point of transition between a straight path section and a helical path section. However, at a point of transition between the helical path section and a following straight path section there is a contracting action between the links. Therefore, if the food products treated by air in the helical path section are still delicate, they can be damaged at said point of transition. Further, traction means engaging the conveyor belt on the downstream side of the helical path section act only on that lateral edge of the belt where the links define a constant pitch. Finally, in a freezing plant freezing together of the belt links may render it difficult to contact said links at the downstream side of the belt pile.